ODME and potential duplicate message

Hello all-

We are using ODME to perform an Office 365 to Office 365 tenant to tenant migration.

Well before we came on site, the customer tried using Bit Titan and copied mailbox data from 2 source to 2 target mailboxes but stopped mid-stream. They abandoned the BT product and here we are with ODME.

My question is fairly simple: If we start a copy from source to target for those 2 mailboxes, will there be duplicates? Do we need to scrub the target mailboxes before we start the copy? 

I am award that folder hierarchies can bring on duplicates if a user makes changes after an initial copy completes but I'm mostly concerned about the "inbox".

As always, your assistance is greatly appreciated.

Regards,

Eric